High Temperature Crosslinked Polysulfones Used for Downhole Devices

ABSTRACT

Thermally crosslinked polysulfone may be made from linear polysulfone, such as polyethersulfone, in powder form blended with a powdered inorganic peroxide such as magnesium peroxide or another oxygen source, to form a mixture followed by compression inside a mold. The mixture is cured at a an elevated temperature, for instance above 325° C., for an effective period of time to form a dense object. The object is then boiled in water, optionally under pressure, to remove the salt to give a structure that is open and porous which may be used as a filtration device on a downhole tool for hydrocarbon recovery. If a powdered salt is not used, a thermally crosslinked, solid, void-free polysulfone is made which may be strong and rigid at ambient, surface temperatures, but is an elastomer at elevated downhole temperatures, and is thus suitable for use as a packer or an O-ring.

TECHNICAL FIELD

The present invention relates to a new class of sulfone polymers andtheir applications such as in filtration devices used in oil and gaswellbores to prevent the production of undesirable solids from theformation, and sealing devices which may be used to seal flow paths toprevent fluid from passing at all. More particularly the inventionrelates to thermally crosslinked sulfone polymers which are strong andrigid at low temperature below glass transition temperature, whichmaterials are also elastically rubbery at high temperature above glasstransition temperature.

TECHNICAL BACKGROUND

Sulfone polymers are linear amorphous thermoplastics commerciallyavailable from companies such as Solvay Plastics. They are widely usedas adhesives, composites, or moldings for use in automobiles, householdappliances, and other applications. As linear amorphous thermoplastics,they tend to creep under load especially at elevated temperature.Furthermore, they are sensitive to various solvents resulting in theirlimits of applications. Attempts to improve sulfone polymers haveincluded crosslinking it. For example, U.S. Pat. No. 4,431,761 discloseda method to chemically replace the end groups of hydroxyl-terminatedpolyethersulfone to give ethynyl-terminated polyethersulfone. U.S. Pat.No. 4,414,269 disclosed a method to have the functional groups ofpolysulfones be derived from condensation products of amino-phenols andacid anhydrides, which are thermally cross-linkable. However, thesemethods require additional chemical reaction steps involving expensivechemicals and solvents. Furthermore, these methods are limited to thosecommercially available polysulfones having functional end group such ashydroxyl-ended polyethersulfone. It is known that polyethersulfone isnot as good as other sulfone polymers, such as polyphenylsulfone, interms of chemical compatibilities. Polyethersulfone tends to degrade invarious fluids at elevated temperature.

In contrast to amorphous thermoplastics, other types of polymers aresemi-crystalline thermoplastics such as polyetheretherketone (PEEK).These polymers can withstand high heat and exposure to causticchemicals. However, these polymers lack elasticity and they are notdesirable to be used as sealing materials. Usually, these materials areused as sealing backup rings.

Fluoroelastomers especially perfluoroelastomers have good thermalstability and excellent chemical resistance. They show rubberyelasticity at a wide range of temperature. Perfluoroelastomers such asKALREZ® made by DuPont are very expensive. Certain grades are claimed tohave a maximum continuous service temperature of 327° C. However, thishas not been verified in practice in downhole applications at hightemperature and high pressure for well life duration. Some of theperfluoroelastomers tend to have cracks during a sudden drop ofpressure.

It would thus be desirable to discover new materials and devices madefrom these materials such as screens to prevent the undesirableproduction of solids and such as seals on downhole packers and the like.

SUMMARY

There is provided, in one form, thermally crosslinked polysulfone madeby heating polysulfone powder in the presence of oxygen to a hightemperature, such as at or above 325° C. inside an oven for at least 8hours. The polysulfone is found to be crosslinked via an oxidizationprocess. The oxygen may come from the air, a pure or impure oxygensource and/or a powdered inorganic peroxide.

Problems have been found when attempting to make a molded part: thesurface is found to be crosslinked, but the internal portion of thematerials is not crosslinked, resulting in non-uniformity within thematerial. It has been discovered herein that a small amount of anoxidant such as magnesium peroxide will result in crosslinking formolded polysulfone parts. Unlike other organic or inorganic peroxidessuch as dicumyl peroxide, benzoyl peroxide, zinc peroxide, calciumperoxide, etc., magnesium peroxide decomposes at much higher temperatureat 350° C., and releases oxygen upon decomposition.

There is provided, in another form, thermally crosslinked polysulfonemade by a process that involves mixing a polyphenylsulfone (PPSU) powderobtained from company Solvay Plastics under the commercial name RADEL® Rand inorganic peroxide powder such as magnesium peroxide at the percentfrom about 0.5% to about 5% of the total polysulfone powder by weight.The mixture containing two powders, polysulfone and peroxide powders,may be heated to 375° C. for at least 8 hours. Whether or not theresultant polysulfone is crosslinked may be determined by examining apiece of material placed in the solvents such as N-methyl-2-pyrrolidone(NMP) or N,N-dimethylformamide (DMF). If material is cross-linked, itdoes not dissolve in the solvent. Dynamic Mechanical Analysis (DMA) mayalso be used to examine whether or not the resultant polysulfone iscrosslinked. The crosslinked polysulfone will maintain a relatively highmodulus at a wide temperature range above its glass transitiontemperature while the linear non-crosslinked polysulfone will quicklydrop its modulus as the temperature is raised higher than its glasstransition temperature.

In another non-limiting embodiment there is provided a method of makingthermally crosslinked polysulfone that involves mixing a polysulfonepowder, where the polysulfone is selected from the group consisting ofpolyethersulfone, polyphenylsulfone, polysulfone and mixtures thereof,with a powdered magnesium peroxide and a powdered salt selected from thegroup consisting of NaCl and/or KCl. The method further concernsoptionally preheating the mixture to a temperature in the range of about140 to about 160° C.; and curing the mixture at a temperature in therange of from about 365 to about 385° C. to crosslink the polysulfone aswell as to fuse polysulfone powder together with salt particles forminga solid part.

Further there is provided in a different, non-restrictive versionwellbore seal that includes a substrate and a thermally crosslinkedpolysulfone on the substrate, where the thermally crosslinkedpolysulfone is made by the method described in the previous paragraphs.The thermally crosslinked polysulfone may not necessarily be anelastomer at surface ambient temperature, but is an elastomer at anelevated temperature in the wellbore.

Additionally, there may be provided in another non-limiting embodiment awellbore filtration device that includes a shape-memory porouspolysulfone material, where the shape-memory porous polysulfone materialhas a compressed position and an expanded position. The shape-memoryporous polysulfone material is maintained in the compressed position ata temperature below its glass transition temperature. The shape-memoryporous polysulfone material expands from its compressed position to itsexpanded position when it is heated to a temperature above its glasstransition temperature. The shapememory porous polysulfone material is athermally crosslinked polysulfone made by the process involving mixing apolysulfone powder, where the polysulfone is selected from the groupconsisting of polyethersulfone, polyphenylsulfone, polysulfone andmixtures thereof, with a powdered magnesium peroxide and a powdered saltselected from the group consisting of NaCl and/or KCl. The processfurther includes compressing the mixture into a mold. The mixture ispreheated to a temperature in the range of about 114 to about 160° C.Subsequently, the mixture is cured at a temperature in the range of fromabout 290 to about 310° C. when sulfur is optionally used as across-linker or the mixture is cured at a temperature in the range offrom about 365 to about 385° C. when magnesium peroxide us used as anoxygen source as a cross-linker to crosslink the polysulfone chains togive a thermally crosslinked polysulfone. Finally, the cured crosslinkedpolysulfone may be boiled in water and the salt is removed therefrom,optionally in a pressurized environment, to recover the shape-memoryporous polysulfone material.

Additionally, there may be provided in another non-limiting embodiment awellbore sealing device that includes a void-free solid polysulfonematerial, the polysulfone material having a thermally crosslinkedpolysulfone may not necessarily be an elastomer or may be a rigidplastic at surface ambient temperature, but is an elastomer at anelevated temperature in the wellbore. The thermally crosslinkedpolysulfone may be manufactured as a tubular shape similar to thepackers widely used on downhole tools to isolate different zones ofdownhole. When hydraulic force is applied at the end of the shape, thetubular rubbery cross-linked polysulfone is expanded in diameter andcontact with borehole wall to seal the gap between inner borehole wallsurface and outside surface of packer.

Additionally, there may be provided in another non-limiting embodiment awellbore sealing device that includes a void-free solid polysulfonematerial. The polysulfone material having a thermally crosslinkedpolysulfone may not necessarily be an elastomer or may be a rigidplastic at surface ambient temperature, but is an elastomer at anelevated temperature above glass transition temperature. When thethermally crosslinked polysulfone is made as a tubular shape and acenter core is placed inside tubular polysulfone material, and also whentubular polysulfone material is pulled from two ends at an elevatedtemperature above the glass transition temperature (T_(g)) at whichmaterial becomes soft and elastic, the length of tubular materialbecomes much longer and the outside diameter of tubular material becomesmuch smaller and the inside diameter of tubular material remains thesame. This stressed shape is able to freeze when temperature is quicklycooled down to ambient temperature well below glass transitiontemperature, and the stressed shape is also able to remain unchangedeven outside pulling force is removed because the material becomes rigidplastic at ambient temperature. When the stressed tubular shape ofthermally crosslinked polysulfone is installed on the downhole tools,and run in downhole, and contacted with fluids at a given temperaturenear or above its glass transition temperature, the stressed tubularshape will recovery to its original manufactured shape, i.e., the lengthwill be reduced and the outside diameter will be increased. Theexpansion of the outside diameter creates a seal between inner wall ofdownhole and the outside surface of sealing element without additionaloperations from well surface.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graphic image of a thermally crosslinked polysulfone foammade in accordance with a method described herein which appearancesuggests a porous rock.

DETAILED DESCRIPTION

Polysulfone is one of the high temperature engineering plastics widelyused as adhesives, composites, or moldings, for use in automobiles,household appliances, and other applications, because it displays avariety of desirable characteristics including durability, thermal,hydrolytic and dimensional stability, low coefficient of thermalexpansion, retention of modulus to temperatures approaching T_(g) andradiation resistance. Polysulfone is a linear amorphous thermoplastic.Thus, it is sensitive to various organic solvents. Many attempts havebeen made to induce molecular crosslinks, but previous attempts requiredchemical synthesis handling various solvents and monomers. Polysulfoneis also made as a porous film or membrane and widely used in the liquidfiltration and separation industries.

Described herein is a new method, making high temperature elastomers orrubbery materials from linear amorphous high temperature thermalplastics such as polyphenylsulfone. These linear amorphous thermalplastics have no functional end groups such as hydroxyl groups, andthere is thus no need to chemically convert the hydroxyl end groups intothermally cross-linkable groups such as ethynyl groups. Furthermore, themethod described herein may make cross-linked polysulfones as porousmaterials to be used as sand control media to prevent undesirableproduction of solids from the formation downhole. These porous tubularmaterials made from cross-linked polysulfones are able to expand tocontact borehole wall when they are contacted with downhole fluids at agiven temperature and for a period of time. Furthermore, this method maymake a solid or void-free cross-linked polysulfone as a sealing element,such as a packer to isolate different zones of the well bore to preventflow from passing through. This sealing element in a generally tubularshape is rigid at surface temperature below the material's glasstransition temperature, but is rubbery (elastomeric) at the downholetemperature above its glass transition temperature. When hydraulic forceis applied at the end, the tubular rubbery cross-linked polysulfones isexpanded in diameter and contacts the borehole wall to seal the gapbetween inner borehole wall surface and the outside surface of packer.Furthermore, the method may be used to make a solid or void-freecross-linked polysulfone as a sealing element having a shape memorycharacteristic. This sealing element in tubular shape is able to run inat diameter smaller than borehole diameter. It is able to expand itsdiameter at downhole at given temperature and at a period of time whenit contacts downhole fluids to recover its original expanded position toseal the gap between the inner wall surface and the outside surface ofsealing element without any operational intervention such as hydraulicforce.

Cross-linked sulfone polymers may be obtained from linear amorphouspolysulfones blended with a small amount of cross-linkers, such asoxygen or oxidant, such as from an inorganic peroxide. Alternatively,cross-linked sulfone polymers are obtained through oxygen in the air.Cross-linked sulfone polymers may be made as open structure porousmaterials. When the temperature reaches near or higher than glasstransition temperature, these rubbery porous sulfone polymers may bemechanically compressed and the volume can be substantially reduced. Thestressed shape can be fixed into a compressed position and maintained,even after the applied mechanic force is removed. The stressed shape mayalso be recovered to its original manufactured shape (i.e. expandedposition) when it is heated to near or above glass transitiontemperature. Applications may be found for these materials, such as areactive filtration device used downhole to prevent the production ofundesirable solids from the formation. The crosslinked sulfone polymerscan also be made as void-free solid materials. Applications may also befound for these materials as a sealing element such as an O-ring or apacker to seal flow paths.

In more detail, thermally crosslinkable polysulfones and methods withoutthe need for additional chemical reaction steps have been discovered.The starting sulfone polymers are not required to have functional groupssuch as hydroxyl groups. Any sulfone polymers may be used, including,but not necessarily limited to, polysulfone, polyethersulfone, orpolyphenylsulfone, which polysulfones undergo a process of oxidationwhen the polymer contacts with oxygen in the air at temperature at least325° C. or above. Some inorganic peroxides such as magnesium peroxidehave been found to participate in oxygen crosslinking with sulfonepolymers. When a small amount of powdered magnesium peroxide is addedinto powdered sulfone polymers, thermal cross-links occurs even withoutcontacting oxygen in the air. Many inorganic or organic peroxides suchas dicumyl peroxide, benzoyl peroxide, zinc peroxide, calcium peroxide,etc., are thermally decomposed at a relative low temperatures rangingfrom 105° C. for benzoyl peroxide to 275° C. for calcium peroxide incomparison with the molding temperature at least 350° C. or above forsulfone polymers. Magnesium peroxide decomposes at much highertemperature, for instance at around 350° C., which is comparable to themolding temperature of sulfone polymers. Therefore, it may be verydesirable to use magnesium peroxide as a crosslinker for sulfonepolymers. In one non-limiting embodiment, the amount of magnesiumperoxide mixed with the polysulfone is from about 0.5 wt % independentlyto about 5 wt %, based on the total amount. Alternatively, the amount ofmagnesium peroxide of total sulfone polymer powder is from 2%independently to 3%.

High temperature crosslinked porous polysulfone foams and methods formaking them have been discovered. These polysulfones have improvedsolvent resistance and will find utility at elevated temperatures, suchas those encountered downhole. For instance, in one non-limitingembodiment the glass transition temperature was measured as 190° C. byDynamic Mechanical Analysis. The open cell structure allows fluid toflow through the material quickly. These materials may be used ondownhole tools as sand control screens, as will be described in detailbelow.

As noted, a three-dimensional open cell cross-linked polysulfone hasbeen discovered. Fluid such as water or oil is able to flow through theporous thermally crosslinked polysulfone quickly. The material is strongand tough. In one non-limiting embodiment, the glass transitiontemperature is measured as about 190° C. using Dynamic MechanicalAnalysis (DMA). The material is not dissolved in the strong solventssuch as N-methyl-2-pyrrolidone (NMP), or N,N-dimethylformamide (DMF),which lack of sensitivity confirms the cross-linked molecular structure.

Example 1

One version of the process involves using commercially available finepolysulfone powders such as UDEL® P-1800 from Solvay Chemicals, Inc. Inone non-limiting embodiment, these polysulfone powders were mixed withliquid one-component thermally degradable polyether polyurethaneprepolymer such as DESMODUR™ E-28 from Bayer Corporation. A small amountof water was added and the mixture started to foam. The water wasfunctioning as a blowing agent. The mixture was then transferred into amold of cylinder shape, followed by curing overnight at 110° C.(pre-heating). After being de-molded, the material was sliced intodiscs, followed by high temperature treatment (curing) at 250° C. fortwo days.

At high temperature, at least 350° C. or above, the polysulfone powdersare fused on polyurethane foam cells forming porous materials while thepolyurethane itself is decomposed. In one non-restrictive version thecombination between polysulfone powder and polyurethane resin was closeto 40:60 by weight to have the best openness. A graphic image of theresulting porous polysulfone is shown in FIG. 1. Another non-limitingexample included adding a blowing agent such as ENOVATE™ 3000 fromHoneywell to increase openness of porous polysulfone.

Originally it was thought that the polyurethane adhesive would be neededto help the material hold its shape. However, it was discovered that thepolyurethane decomposes to give ash which creates an interface thatweakens the material.

There is provided, in one non-restrictive form, thermally crosslinkedpolysulfone made by a process that involves mixing a polyphenylsulfonepowder obtained from company Solvay Plastics under commercial name asRADEL® R and magnesium peroxide at the percent from 0.5 to 5% of thetotal polysulfone powder by weight. The equipment for mixing these twopowders, polysulfone and magnesium peroxide, be a single- ordouble-bladed KITCHENAID mixer or RESODYN type mixer from companyResodyn Corporation. The mixture containing the polysulfone andmagnesium powders was poured into a mold containing a bottom plate and acenter ring, and then placed inside an oven to heat to 150° C. for twohours; followed by 250° C. for 2 hours and finally heated to 375° C. for20 hours. The mixture, including the mold, was taken out of the oven,and a center rod, which was pre-heated to 375° C. was placed inside thecenter ring, followed by compressing via a hydraulic press. The materialmade by compression was a void-free solid. It was rigid at ambienttemperature, but showed rubbery (elastomeric) properties at hightemperature above its glass transition temperature, i.e. above 220° C.Alternatively, the mixture containing the polysulfone and magnesiumpowders is poured into an extruder such as a RINGEXTRUDER from Century,Inc. Inside the extruder, materials are melted and mixed between screwsrotating in opposite directions from each other at temperature at orabove 375° C. Materials may be squeezed out through a die and moldedinto sheets for testing, or, alternatively through a die and then cutinto individual pellets. The pellets may be molded into sheets ordesired parts for evaluation or finished products.

Example 2

In another non-limiting embodiment, thermal cross-linkable sulfonepolymer was made from the commercially available polyphenylsulfonepowder obtained from company Solvay Plastics under commercial name asRADEL® R and magnesium peroxide at the percent from 0.5 to 5% of thetotal polysulfone powder by weight. This material in powder form wasblended with a powdered salt, in one case sodium chloride, followed bycompression inside tubular mold.

The mixture or material was pre-heated at 120° C. and then cured at 375°C. to form a dense disc. This material was then boiled in water in thepressurized or compressed container. The salt was removed by boiling itoff. While it is not necessary that the salt removal be conducted underpressure, it speeds up the salt removal process. After all the salt wasremoved, the material was very open and porous. Differential pressurethrough open flow test was measured as 0.06 psi (0.4 kPa). Thiscross-linked porous polyethersulfone showed good elasticity at atemperature above its glass transition temperature (T_(g)) 232.2° C., asmeasured by DMA.

Once the disc was compressed at high temperature above T_(g), the volumewas greatly reduced. This changed shape at high temperature above T_(g)can be frozen when temperature is quickly cooled down well below itsT_(g). Also, this changed shape can be retained sufficiently long enougheven when the outside compressive force is removed. When materials areheated to high temperature above T_(g), the shape can be fully recoveredto its original shape. Thus, the thermally crosslinked polysulfone mayfunction as a shape-memory porous polysulfone material. The cross-linkedporous sulfone polymer has very good hydrolytic resistance and iswell-compatible with various downhole fluids at high temperature.

Molecular cross-linking occurs at temperature 325° C. or higher. Theresulting cross-linked sulfone polymer is not dissolved in the solventssuch as NMP or DMA. Materials show good elasticity at temperature aboveglass transition temperature 232.2° C., measured by DMA in onenon-limiting example.

More specifically, suitable powdered polysulfones include, but are notnecessarily limited to polyethersulfone, polyphenylsulfone, polysulfoneitself, and mixtures thereof.

In one non-limiting optional embodiment, oxygen in the air mayparticipate as a crosslinker without any chemical modification (that is,without conversion of the hydroxyl termination to ethynyl termination)if the curing is conducted in a range of from about 325° C. to about400° C. Alternatively the temperature may be 350° C. or above, or inanother non-restrictive embodiment 375° C. or above. This crosslinkingbegins at the surface of the material does not penetrate into theinterior unless the material is mixed so that air or oxygen reaches theinterior. The use of oxygen or oxidants as a crosslinker is particularlyuseful for sulfone polymers.

The powdered salt employed may include, but is not necessarily limitedto NaCl, KCl, and combinations thereof.

In one non-limiting embodiment the weight ratio of powdered salt topolysulfone powder ranges from about 80:20 independently to about 50:50,alternatively from about 70:30 independently to about 60:40, whereby“independently”it is meant that any upper threshold may be combined withany lower threshold to obtain a valid alternative range.

The compressing of the mixture into a mold and the boiling of thematerial in the mold may be conducted at a pressure above atmospheric inthe range of from about 0 independently to about 0.1 MPa, alternativelyfrom about 0.07 independently to about 0.1 MPa. The boiling may beconducted at a temperature in the range of from about 100 independentlyto about 121° C., alternatively from about 113 independently to about121° C. As noted, boiling to remove the salt is optionally done underpressure because the removal process is faster.

Alternatively, in the mixing of the polysulfone powder with a saltpowder, a liquid polyurethane adhesive may be optionally included in themixing in an amount ranging from about 1 independently to about 10% oftotal polysulfone powder weight based on the total mixture;alternatively from about 2 independently to about 5 wt % of totalpolysulfone powder weight based on the total mixture.

In one non-limiting embodiment, the thermally crosslinked polysulfoneswhich are not porous or blown with a blowing agent may be used as seals,in a non-restrictive instance as high temperature wellbore seals.Interestingly, at ambient temperatures on the surface, the thermallycrosslinked polysulfone may not necessarily be elastomers, but they areelastomers at the relatively high temperatures downhole where they needto function as an elastomeric seal; for instance from about 220 to about350° C. Thermally crosslinked polysulfones may be used as sealingmaterials, including but not necessarily limited to packers or O-rings,for any downhole temperature ranging from 220° C. or above at thetemperature above the material's glass transition temperature.Alternatively, thermally crosslinked polysulfones may be used as sealingmaterials, including but not necessarily limited to, backup rings orstructural parts, below 220° C. at the temperature below material'sglass transition temperature. Typically, the thermally crosslinkedpolysulfone would be formed or placed on a substrate, such as a tubulargood or downhole tool and located in place where the seal is needed.

Downhole tools and, in particular, filtration devices for downhole sandcontrol using the thermally crosslinked, porous polysulfones, aredisclosed herein. The filtration devices include the thermallycrosslinked, porous as one or more shape-memory materials that are runinto the wellbore in a compressed shape or position. The shape-memorypolysulfone material remains in the compressed shape induced on it aftermanufacture at ambient surface temperature or at wellbore temperatureduring run-in. After the filtration device having the shape-memorypolysulfone material is placed at the desired location within the well,the shape-memory polysulfone material is allowed to expand to itsprecompressed shape, i.e., its original, manufactured shape, at downholetemperature at a given amount of time. The expanded shape or setposition, therefore, is the shape of the shape-memory polysulfonematerial after it is manufactured and before it is compressed. In otherwords, the shape-memory material possesses hibernated shape-memory thatprovides a shape to which the shape-memory polysulfone materialnaturally takes after its manufacturing when it is deployed downhole.

As a result of the shape-memory polysulfone material being expanded toits set position, the completely

More specifically, the shape-memory polysulfone foam material is capableof being mechanically compressed substantially, e.g., from about 20 toabout 30% of its original volume, at temperatures above its glasstransition temperature (T_(g)) at which the material becomes soft. Whilestill being compressed, the material is cooled down well below itsT_(g), or cooled down to room or ambient temperature, and it is able toremain at a compressed state even after the applied compressive force isremoved. When the material is heated near or above its T_(g), it iscapable of recovery to its original un-compressed state or shape. Inother words, the shape-memory material possesses hibernated shape-memorythat provides a shape to which the shape-memory material naturally takesafter its manufacturing. The compositions of polysulfone foam are ableto be formulated to achieve desired glass transition temperatures whichare suitable for the downhole applications, where deployment can becontrolled for temperatures below T_(g) of filtration devices at thedepth at which the assembly will be used.

It has been discovered herein that the thermal stability and solventresistance are significantly improved when the polysulfone are thermallycross-linked as previously discussed. The compositions of polysulfonefoam are able to be formulated to achieve different glass transitiontemperatures within the range from 190° C. to 240° C., which isespecially suitable to meet most downhole application temperaturerequirements. This range is higher than that of some other shape-memoryfoams, such as certain types of polyurethane foams. It is useful to havedifferent foams with different T_(g)s to give the design engineer moreoptions.

In one specific non-limiting embodiment, the shape-memory material is apolysulfone foam material that is extremely tough and strong and that iscapable of being compressed and returned to substantially its originalexpanded shape. The T_(g) of the shape-memory polysulfone foam in onenon-limiting embodiment may be about 232.2° C. and it may be compressedby mechanical force at 250° C., in another non-limiting embodiment.While still in compressed state, the material is cooled down to roomtemperature. The shape-memory polysulfone foam is able to remain in thecompressed state even after applied mechanical force is removed. Whenmaterial is heated to about 250° C., it is able to return to itsoriginal shape within 20 minutes. However, when the same material isheated to a lower temperature such as 200° C. for about 40 hours, itremains in the compressed state and does not change its shape.

Factors affecting the T_(g) of the crosslinked polysulfone, whether ornot it is a foam, include the molecular weight of the crosslinkedpolysulfone. By formulating shape-memory porous polysulfone materialusing these different factors, different glass transition temperaturesof shape-memory polysulfone foam may be achieved. Compositions of ashape-memory polysulfone foam material having a specific T_(g) may beformulated based on actual downhole deployment/application temperature.Usually, the T_(g) of a shape-memory polysulfone foam is designed about20° C. higher than actual downhole deployment/application temperature.Because the application temperature is lower than T_(g), the materialretains good mechanical properties.

Further, when it is described herein that the filtration device “totallyconforms” to the borehole, what is meant is that the shape-memory porousmaterial expands or deploys to fill the available space up to theborehole wall. The borehole wall will limit the final, expanded shape ofthe shape-memory polysulfone porous material and in fact not permit itto expand to its original, expanded position or shape. In this wayhowever, the expanded or deployed shape-memory material, being porous,will permit hydrocarbons to be produced from a subterranean formationthrough the wellbore, but will prevent or inhibit small or fine solidsfrom being produced since they will generally be too large to passthrough the open cells of the porous material.

It is to be understood that the invention is not limited to the exactdetails of construction, operation, exact materials, or embodimentsshown and described, as modifications and equivalents will be apparentto one skilled in the art. Accordingly, the invention is therefore to belimited only by the scope of the appended claims. Further, thespecification is to be regarded in an illustrative rather than arestrictive sense. For example, specific combinations of polysulfonepowders, inorganic peroxides, salts and other components and heatingsteps to make the thermally crosslinked polysulfone, specific downholetool configurations and other compositions, components and structuresfalling within the claimed parameters, but not specifically identifiedor tried in a particular method or apparatus, are anticipated to bewithin the scope of this invention.

The terms “comprises” and “comprising” in the claims should beinterpreted to mean including, but not limited to, the recited elements.

The present invention may suitably comprise, consist or consistessentially of the elements disclosed and may be practiced in theabsence of an element not disclosed. For instance, the thermallycrosslinked polysulfone may be made by a process consisting of orconsisting essentially of mixing a polysulfone powder, where thepolysulfone is as defined in the claims, with powdered inorganicperoxide and optionally a powdered salt as described in the claims;optionally preheating the mixture to a temperature in the range of about110 to about 130° C. and curing the mixture at a temperature above about325° C. to crosslink the polysulfone to give a crosslinked polysulfone.The process for making thermally crosslinked polysulfone may consist ofor consist essentially of these steps. Furthermore, the process formaking the shape-memory porous polysulfone material may consist of orconsist essentially of the above steps, but also further consist of orconsist essentially of boiling the cured crosslinked polysulfone inwater and removing the salt therefrom to recover a porous crosslinkedpolysulfone, with or without pressure.

1. Thermally crosslinked polysulfone made by a process comprising:mixing a polysulfone powder, where the polysulfone powder is selectedfrom the group consisting of polyethersulfone, polyphenylsulfone,polysulfone and mixtures thereof, with oxygen from a source selectedfrom the group consisting of air, oxygen and a powdered inorganicperoxide; and heating the mixture at a temperature above about 325° C.for a time period effective to crosslink the polysulfone with oxygen togive a thermally crosslinked polysulfone.
 2. The thermally crosslinkedpolysulfone of claim 1 where the time period is at least eight hours. 3.The thermally crosslinked polysulfone of claim 1 where the inorganicperoxide is magnesium peroxide.
 4. The thermally crosslinked polysulfoneof claim 1 where heating the mixture is at a temperature above about350° C.
 5. The thermally crosslinked polysulfone of claim 1 where theprocess further comprises compressing the mixture into a mold aftermixing and prior to heating.
 6. The thermally crosslinked polysulfone ofclaim 1 where the process further comprises mixing the polysulfonepowder and the powdered inorganic peroxide with a powdered salt selectedfrom the group consisting of NaCl, KCl, and combinations thereof, andafter heating to give the thermally crosslinked polysulfone, boiling thecured crosslinked polysulfone in water and removing the salt therefromto recover a porous crosslinked polysulfone.
 7. The thermallycrosslinked polysulfone of claim 6 where the boiling is conducted at atemperature in the range of from about 100 to about 121° C. and thepressure ranges from about 0 to about 0.1 MPa.
 8. The thermallycrosslinked polysulfone of claim 6 where the porous crosslinkedpolysulfone can pass fluids therethrough at a differential pressure of0.1 psi or less.
 9. The thermally crosslinked polysulfone of claim 6where the weight ratio of powdered salt to polysulfone powder rangesfrom about 80:20 to about 50:50.
 10. The thermally crosslinkedpolysulfone of claim 1 where in the mixing of the polysulfone powderwith a salt powder, a liquid polyurethane adhesive is included in themixing in an amount ranging from about 1 to about 10 wt % based on thetotal polysulfone powder weight.
 11. A process for making thermallycrosslinked polysulfone comprising: mixing a polysulfone powder, wherethe polysulfone powder is selected from the group consisting ofpolyethersulfone, polyphenylsulfone, polysulfone and mixtures thereof,with oxygen from a source selected from the group consisting of air,oxygen and a powdered inorganic peroxide; and heating the mixture at atemperature above about 325° C. to crosslink the polysulfone with oxygento give a thermally crosslinked polysulfone.
 12. The process of claim 11where the time period is at least eight hours.
 13. The process of claim11 where the inorganic peroxide is magnesium peroxide.
 14. The processof claim 11 where heating the mixture is at a temperature above about350° C.
 15. The process of claim 11 further comprising compressing themixture into a mold after mixing and prior to heating.
 16. The processof claim 11 further comprising mixing the polysulfone powder and thepowdered inorganic peroxide with a powdered salt selected from the groupconsisting of NaCl, KCl, and combinations thereof, and after heating togive the thermally crosslinked polysulfone, boiling the curedcrosslinked polysulfone in water and removing the salt therefrom torecover a porous crosslinked polysulfone.
 17. The process of claim 16where the boiling is conducted at a temperature in the range of fromabout 100 to about 121° C. and the pressure ranges from about 0 to about0.1 MPa.
 18. The process of claim 11 where in the mixing of thepolysulfone powder with a salt powder, a liquid polyurethane adhesive isincluded in the mixing in an amount ranging from about 1 to about 10 wt% based on the total polysulfone powder weight.
 19. The process of claim16 where the weight ratio of powdered salt to polysulfone powder rangesfrom about 80:20 to about 50:50.
 20. A wellbore seal comprising: asubstrate; and a thermally crosslinked polysulfone on the substrate,where the thermally crosslinked polysulfone is made by the processcomprising: mixing a polysulfone powder, where the polysulfone powder isselected from the group consisting of polyethersulfone,polyphenylsulfone, polysulfone and mixtures thereof, with oxygen from asource selected from the group consisting of air, oxygen and a powderedinorganic peroxide; and heating the mixture at a temperature above about325° C. to crosslink the polysulfone with oxygen to give a thermallycrosslinked polysulfone; where the thermally crosslinked polysulfone maynot be an elastomer at surface ambient temperature, but is an elastomerat an elevated temperature in the wellbore.
 21. The wellbore seal ofclaim 20 where the elevated temperature in the wellbore is in the rangeof about 220 to about 350° C.
 22. A wellbore filtration devicecomprising: a shape-memory porous polysulfone material, the shape-memoryporous polysulfone material having a compressed position and an expandedposition, where the shape-memory porous polysulfone material ismaintained in the compressed position at a temperature below its glasstransition temperature, where the shape-memory porous polysulfonematerial expands from its compressed position to its expanded positionwhen it is heated to a temperature above its glass transitiontemperature, where the shape-memory porous polysulfone material is athermally crosslinked polysulfone made by the process comprising: mixinga polysulfone powder, where the polysulfone powder is selected from thegroup consisting of polyethersulfone, polyphenylsulfone, polysulfone andmixtures thereof, with oxygen from a source selected from the groupconsisting of air, oxygen and a powdered inorganic peroxide and apowdered salt selected from the group consisting of NaCl, KCl, andcombinations thereof, compressing the mixture into a mold; heating themixture at a temperature above about 325° C. for a period of timeeffective to crosslink the polysulfone to give a crosslinkedpolysulfone; and boiling the cured crosslinked polysulfone in water andremoving the salt therefrom to recover the shape-memory porouspolysulfone material.
 23. The wellbore filtration device of claim 22where in the process of making the thermally crosslinked polysulfone,the boiling is conducted at a temperature in the range of from about 100to about 121° C. and the pressure ranges from about 0 to about 0.1 MPa.